In the latter system, a high definition wide aspect ratio (e.g. 16:9, also referred to as 5-1/3:3) single channel signal is decomposed into a center image signal and an enhancement signal. The center image signal is transmitted via a first channel in standard NTSC format and when received by a standard NTSC television receiver, produces the center image having a 4:3 aspect ratio The enhancement signal is transmitted via a second channel. The enhancement signal contains information for side panel images which, together with the center image signal, reproduce the original wide aspect ratio image. The enhancement signal also carries additional information for the center image that cannot be accommodated by a standard NTSC signal. This additional or enhancement information, when properly combined with the NTSC center image signal, restores the high definition that was "lost" when the center image signal was converted to a standard NTSC signal. Additional video and audio enhancement information may be carried by the enhancement signal on the second channel. Such a two channel NTSC-compatible system is described in U.S. patent application, Ser. No. 06/856,622 filed Apr. 25, 1986, now U.S. Pat. No. 4,694,339 in the name of Mikhal Tsinberg, common assignee.
In order to acceptably reproduce the full high definition wide aspect ratio picture transmitted by the two-channel system, it is necessary to have a receiver that receives both the first and second channel signals and properly stitches them back together so smoothly that the stitch is not observable by viewers. This requires that any phase difference between the first and second channel signals be compensated for and that the black level, white level and chrominance (hue and saturation) be reproduced equally for both channel signals so that no variation in brightness, contrast, hue or saturation is introduced by the process of decomposing the original high definition wide aspect ratio image into two signals, transmitting them via two separate channels, and recombining them to produce the display at the receiver.